<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>

<script>
    // 异步（不等待）
    setTimeout(()=>{
        console.log('定时执行');
    },3000)

    console.log('哈哈哈');
</script>

<!--js文件是同步（等待）加载的-->
<script src="jquery.js"></script>
<script src="b.js"></script>


</body>
</html>